Aerofoil and a method for construction thereof

ABSTRACT

An aerofoil and a method for construction of the aerofoil are provided. The aerofoil has an outer wall and an inner wall, wherein the walls are separated by a cooling channel, and a coolant fluid is guidable through the cooling channel during the operation of the aerofoil. The inner wall is provided with a protrusion, which is profiled and arranged such that it extends from the inner wall into the cooling channel. The protrusion directs at least a part of the coolant fluid to impinge the coolant fluid on a first region of the outer wall.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2013/072388 filed Oct. 25, 2013, and claims the benefitthereof. The International Application claims the benefit of EuropeanApplication No. EP12190807 filed Oct. 31, 2012. All of the applicationsare incorporated by reference herein in their entirety.

FIELD OF INVENTION

The present invention relates to an aerofoil and a method forconstruction of the aerofoil.

BACKGROUND OF INVENTION

An aerofoil is generally used as a vane and/or a blade in a turbomachinesuch as a gas turbine or a steam turbine for power generation. Theturbomachine operates for extensive periods of time, and during itsoperation the aerofoil comes into contact with very high temperaturegases (in excess of 1000° C.), i.e. the working fluid in theturbomachine. Therewith the temperature of the external surface of theaerofoil increases tremendously. Exposure of the aerofoil to thetremendously high operating temperatures for such extensive periods oftime leads to a reduction of the operational life span of the aerofoil.Thus, the aerofoil needs to be cooled during its operation forincreasing its operational life span.

Impingement cooling is a popular technique that is employed for coolingan aerofoil. In impingement cooling, a coolant fluid is bombarded athigh pressure onto certain regions (hot spots) on the aerofoil thatrequire cooling. This requires the coolant fluid to be provided withhigh pressure for producing the impingement, which requires theemployment of additional means to increase the coolant fluid pressure.Therefore, the current impingement cooling technique is expensive aswell as not efficient for cooling the aerofoil.

U.S. Pat. No. 5,704,763 discloses an airfoil with a subdivided coolingpassageway including arrangements for creating turbulences of a coolingfluid directed through the passageway. The turbulences improve thecooling efficiency.

U.S. Pat. No. 7,722,327 proposes an alternative technique for cooling anaerofoil, and recites a multiple vortex cooling circuit for a thinaerofoil, wherein a wall of the aerofoil is constructed with a pluralityof individual vortex cooling channels that are connected to a leadingedge cooling air supply channel. This is however a very expensivesolution, because it advocates an intricate aerofoil structure, therebyincreasing the complexity of construction of the aerofoil.

SUMMARY OF INVENTION

An objective of the present invention is to propose a simpler and anenhanced design of an aerofoil for improving the efficiency of coolingthe aerofoil.

The above objective is achieved by an aerofoil and a method forconstruction of the aerofoil according to the independent claims.

The underlying objective of the present invention is to propose a designfor an aerofoil such that the cooling of the aerofoil, especially duringthe operation of the aerofoil, is enhanced. Herein, the aerofoilaccording to the present invention comprises an outer wall, an innerwall, and a cooling channel located between the aforementioned walls.The cooling channel is purported to guide a coolant fluid during theoperation of the aerofoil. The inner wall comprises a protrusion, whichextends from a surface of the inner wall and into the cooling channel.This protrusion is arranged and profiled so as to direct at least a partof the coolant fluid, which is flowing through the cooling channel andespecially over the protrusion, to impinge the coolant fluid on to afirst region of the outer wall. Furthermore, the outer wall comprises aprotrusion, which extends from a surface of the outer wall and into thecooling channel. The protrusion on the outer wall is also arranged andprofiled so as to direct at least a part of the coolant fluid, which isflowing through the cooling channel and especially over the protrusionon the outer wall, to impinge the coolant fluid on to a second region ofthe inner wall.

The protrusion aids in directing the coolant fluid for producing animpingement of the coolant fluid on the outer wall. The impingement ofthe coolant fluid on the outer wall purports to transfer more the heatfrom the outer wall on to the coolant fluid, especially compared to theconventional technique of convection cooling. Additionally, by providinga protrusion, the effective surface area of the wall is increased,thereby enhancing the transfer of heat from the outer wall to thecoolant fluid. Therewith, it is possible to redirect the coolant fluidimpinging on the outer wall back on to the inner wall during thecirculation of the coolant fluid inside the cooling channel, therebypreparing the coolant fluid to be directed again on to the outer wall tocause an impingement of the coolant fluid on a different location on theouter wall.

Thereby an enhanced cooling of the outer wall is achieved, especiallythe cooling of the first region.

According to an embodiment of the invention disclosed herein, theprotrusion on the inner wall extends both in a direction of flow of thecoolant fluid and in a direction towards the outer wall.

According to another embodiment of the invention disclosed herein, theprotrusion comprises an ascending portion, a descending portion and apeak, when perceived in an overall direction of flow of the coolantfluid. The ascending portion ascends in a direction towards the outerwall, whereas the descending portion descends in a direction towards theinner wall. The peak is located between the ascending portion and thedescending portion. Additionally, an absolute value of a gradient of thedescending portion is greater than an absolute value of a gradient ofthe ascending portion.

This profile of the protrusion according to the preceding embodiments isadvantageous in smoothly directing the coolant fluid on to the firstregion on the outer wall. The gradient of the ascending portion smoothlyguides the coolant fluid along the ascending portion in a manner forincreasing the efficacy of the impingement of the coolant fluid on tothe first portion of the outer wall. Therewith, both efficaciousimpingements as well as an unobstructed circulation of the coolant fluidin the cooling channel are achieved.

According to yet another embodiment of the invention disclosed herein,the location of the protrusion in the aerofoil is such that it isproximal to a leading edge of the aerofoil. The leading edge of theaerofoil undergoes more heating than the trailing edge of the aerofoilduring the operation of the aerofoil. Therefore, by dint of theprotrusion being located closer to the leading edge, the protrusionpurports to cool down the part of the aerofoil that undergoes moreheating, thereby increasing the operational life span of the aerofoil.

According to yet another embodiment of the invention disclosed herein,the protrusion on the outer wall extends both in a direction of flow ofthe coolant fluid and in a direction towards the inner wall.

According to yet another embodiment of the invention disclosed herein,the protrusion on the outer wall also comprises an ascending portion, adescending portion and a peak, when perceived in an overall direction offlow of the coolant fluid. The ascending portion ascends in a directiontowards the inner wall, whereas the descending portion descends in adirection towards the outer wall. The peak is located between theascending portion and the descending portion. Additionally, an absolutevalue of a gradient of the descending portion is greater than anabsolute value of a gradient of the ascending portion.

This profile of the protrusion on the outer wall that is in accordancewith any of the preceding embodiments is advantageous in smoothlydirecting the coolant fluid impinging on to the first region on theouter wall back to the second region on the inner wall. The gradient ofthe ascending portion smoothly guides the coolant fluid along theascending portion in a manner for increasing the efficacy of theimpingement of the coolant fluid on to the second portion of the innerwall. Therewith, both efficacious impingements as well as anunobstructed circulation of the coolant fluid in the cooling channel areachieved. Furthermore, this is beneficial in causing a series ofimpingements of the coolant channel on the outer wall, thereby aiding inincreasing the efficiency of cooling the outer wall.

According to yet another embodiment of the invention disclosed herein,when perceived in the overall direction of flow of the coolant fluid,the location of the protrusion on the outer wall and the location of theprotrusion on the inner wall such that the part of coolant fluid that isdirected towards the first region by the protrusion on the inner wallimpinges on the ascending portion of the protrusion on the outer wall.Therewith, it is possible to cause a more efficient and a smoother flowpath of the coolant fluid in the cooling channel.

According to yet another embodiment of the invention disclosed herein,when perceived in the overall direction of flow of the coolant fluid,the peak of the protrusion on the inner wall and the peak of theprotrusion on the outer wall are offset to one another. Therewith, itenhances the smoothness of the flow as well as the efficacy of theseries impingements of the coolant fluid between the walls of theaerofoil.

According to yet another embodiment of the invention disclosed herein,the location of the protrusion on the outer wall is such that it isproximal to the leading edge of the aerofoil. Therewith, it benefits thecooling of the parts of the aerofoil located proximal to the leadingedge, because the leading edge of the aerofoil undergoes maximum heatingduring the operation of the aerofoil. This purports to increase theoperational life span of the aerofoil.

In a method for construction of the aerofoil according to any of theaforementioned embodiments, the outer wall and the inner wall arearranged such that the cooling channel separates the outer wall and theinner wall. The protrusion on the inner wall is provided such that theprotrusion (70) on the inner wall extends from the surface of the innerwall and into the cooling channel. Furthermore, the protrusion on theouter wall is provided such that the protrusion on the outer wallextends from the surface of the outer wall and into the cooling channel.Therewith, it is possible to directing at least a part of the coolantfluid flowing through the cooling channel and also over the protrusionon the outer wall for impinging the on to a second region of the innerwall.

Therewith, it is beneficial in directing the coolant fluid for producingan impingement of the coolant fluid on the first region on the outerwall.

The aforementioned and other embodiments of the invention related to anaerofoil and a method for cooling thereof will now be addressed withreference to the accompanying drawings of the present invention. Theillustrated embodiments are intended to illustrate, but not to limit theinvention. The accompanying drawings contain the following figures, inwhich like numbers refer to like parts, throughout the description anddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The figures illustrate in a schematic manner further examples of theembodiments of the invention, in which:

FIG. 1 depicts a cross-sectional view of an aerofoil according to anembodiment of the present invention,

FIG. 2 depicts an enlarged cross-sectional view of a section of theaerofoil referred to in FIG. 1, and

FIG. 3 depicts a flowchart of a method for construction of the aerofoilreferred to in FIG. 1.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 depicts a cross-sectional view of an aerofoil 10 in accordancewith one or more embodiments of the invention described herein. Theaerofoil 10 can be a vane or a blade of a turbomachine (not depicted),such as a gas turbine or a steam turbine that is employed for powergeneration.

The aerofoil 10 comprises a first wall 20, a second wall 30, and acooling channel 40. The cooling channel 40 is located between the firstwall 20 and the second wall 30, and the cooling channel 40 facilitatesthe cooling of first wall 20 of the aerofoil 10. The first wall 20 is anouter wall and the second wall 30 is an inner wall of the aerofoil 10,wherein the outer wall 20 surrounds the inner wall 30. Furthermore, thecooling channel 40 separates the inner wall 30 and the outer wall 20. Inaccordance with an exemplary aspect, the cooling channel 40 can surroundthe entire extent of the inner wall 30. However in the exemplaryaerofoil described herein, the inner wall 30 is a core of the aerofoil10.

During the operation of the turbomachine, the outer wall 20 is exposedto hot gases 50 thereby resulting in the heating of the outer wall 20,which subsequently increases the temperature of the outer wall 20. Acoolant fluid 60, which is dispensed into the cooling channel 40, flowsthrough the cooling channel 40. The dispensation of the coolant fluid 60into the cooling channel 40 of the aerofoil 10 is however a well-knowntechnique and is not covered herein for the purpose of brevity.

While the coolant fluid 60 passes through the cooling channel 40, thecoolant fluid 60 is in thermal contact with both the outer wall 20 andthe inner wall 30. The inner wall 30 is relatively cooler than the outerwall 20. The interaction between the coolant fluid 60 and the outer wall20 results in a substantial transfer of heat from the outer wall 20 tothe coolant fluid 60, thereby resulting in the cooling of the outer wall20. The majority of heat would be removed from the aerofoil 10 togetherwith the coolant fluid 60 as described below. Moreover, since thecoolant fluid 60 is in contact with the outer wall 20 as well as theinner wall 30, the cooling channel 40 is capable of transferring amarginal amount of heat onto the inner wall 40. However, the majority ofthe heat transferred from the outer wall 20 onto the coolant fluid 60 isstill retained in the coolant fluid 60. Therewith, the cooling the outerwall 20 is achieved in accordance with the aforementioned manner.

The coolant fluid 60 can be dispensed into the cooling channel 40 usingany of the well-known techniques, for example, by means of a coolantfluid supply (not depicted) operably coupled to an inlet hole 45provided on a base or a root (not depicted) of the aerofoil 10.Thereafter the coolant fluid 60 flows through the cooling channel 40,and the coolant fluid 60 finally exits thorough an exit hole 165 that isgenerally located in the trailing edge 160 of the aerofoil 10. Thecoolant fluid 60 thereby circulates inside the cooling channel 40 byentering into the aerofoil 10 through the inlet hole 45 and by exitingthrough the exit hole 165. Herewith, the majority of heat is transportedout of the aerofoil 10 by means of circulating the coolant fluid 60 inthe cooling channel 40 of the aerofoil 10.

With reference to the exemplary aerofoil 10 depicted in FIG. 1, in theupper half 110 of the aerofoil 10, which is both above the camber line100 and proximal to the suction side 130 of the aerofoil 10, the coolantfluid 60 generally flows towards the leading edge 150 of the aerofoil10. On the other hand, in the lower half 120 of the aerofoil 10, whichis both below the camber line 100 and proximal to the pressure side 140of the aerofoil 10, the coolant fluid 60 generally flows towards thetrailing edge 160 of the aerofoil 10.

To increase the efficiency of the transfer of heat between the outerwall 20 and the coolant fluid 60 for cooling the outer wall 20, aportion 35 of the inner wall 30 comprises a plurality of protrusions70,75. The protrusions 70,75 on the inner wall 30 are advantageouslyintegral to the inner wall 30. Herein, each of the protrusions 70,75 onthe inner wall 30 extends from a surface 37 on the inner wall 30 intothe cooling channel 40 and generally in a direction towards the outerwall 20. These protrusions 70,75 on the inner wall influence the courseof the coolant fluid 60 flowing in the cooling channel 40. Each of theprotrusions 70,75 on the inner wall 30 is arranged and profiled suchthat the coolant fluid 60 is directed towards an opposing first region64 on the outer wall 20, in order to impinge the coolant fluid 60 onthat first region 64 on the outer wall 20. An impingement cooling effecton the opposing first region 64 is therewith achieved since the coolantfluid 60 is provided with increased pressure on the first region 64.This impingement of the coolant fluid 60 on the first region 64 hereinresults in an enhanced transfer of heat from the first region 64 on theouter wall 20 on to the coolant fluid 60. The portion 35 of the innerwall 30 comprising the protrusions 70,75 is advantageously locatedproximal to the leading edge 150 of the aerofoil 10 because of thesignificant heating experienced at the leading edge 150 of the aerofoil10.

Similarly, a portion 25 of the outer wall 20 also comprises a pluralityof protrusions 80,85, wherein each of the protrusions 80,85 on the outerwall 20 extends from a surface 27 on the outer wall 20 into the coolingchannel 40 and generally in a direction towards the inner wall 30. Theprotrusions 80,85 on the outer wall 20 are advantageously integral tothe outer wall 20. Each of the protrusions 80,85 on the outer wall 20 isarranged and profiled such that at least a part of the coolant fluid 60that impinges on the first region 64 on the outer wall 20 is directedtowards an opposing second region 66 on the inner wall 30, therebyproducing an impingement cooling effect on the second region 66 on theinner wall 30, therewith resulting in a marginal transfer of heat fromthe coolant fluid 60 to the inner wall 30. However, the majority of theheat is still retained in the coolant fluid 60.

Herein, the inner wall 30 and the outer wall 20 may comprise arespective plurality of protrusions 70,75,80,85, such that severalcorresponding first regions 64 and second regions 66 are present on theouter wall 20 and the inner wall 30 onto which the coolant fluid wouldbe directed to achieve impingement cooling effect on the first regions64 and second regions 66.

Herein, with the arrangement of the plurality of protrusions 70,75,80,85both on the inner wall 30 and the outer wall 20, the impinged coolantfluid is repeatedly redirected between the outer wall 20 and the innerwall 30 in an overall flow direction of the coolant fluid 60 in thecooling channel 40. For example, if the first protrusion 70,75 islocated on the inner wall 30 as viewed in the overall flow direction,the coolant fluid 60 is directed to impinge on the first region 64 onthe outer wall 20. Thereafter, the coolant fluid 60 is redirectedtowards the opposing second region 66 on the inner wall 30 for furtherimpingement of the coolant fluid 60 on the inner wall 30. Thereafter,the coolant fluid 60 will be again redirected towards the first region64 of the outer wall, and so on. Especially, this series of impingementsof the coolant fluid 60 on the outer wall 20 of the aerofoil 10 resultin enhancing the efficiency of cooling of the aerofoil 10. Furthermore,this portion 25 of the outer wall 20 comprising the protrusions 70,75 isagain advantageously located proximal to the leading edge 150 of theaerofoil 10.

In the upper half 110 of the aerofoil 10, the overall direction of flowof the coolant fluid 60 in the cooling channel 40 of the exemplaryaerofoil 10 depicted herein is in a direction advantageously from thetrailing edge towards the leading edge 150. However, the local directionof the flow of the coolant fluid 60 is determined by the profile of eachof the protrusions 70,75,80,85 over which the coolant fluid 60 flows.

An exemplary section 65 of the aerofoil 10 depicting the hereinabovementioned portions 25,35 of the outer wall 20 and the inner wall 30 andthe cooling channel 40, which is present between the portions 25,35 andthe walls 20,30, is elucidated with reference to FIG. 2. The series ofimpingements of the coolant fluid 60 on the outer wall 20 of the section65 takes place due to the coolant fluid 60 flow over the protrusions70,75 on the inner wall 30 of the section 65. Similarly, the series ofimpingements of the coolant fluid 60 on the inner wall 30 of the section65 takes place due to the coolant fluid 60 flow over the protrusions80,85 on the outer wall 20 of the section 65. The geometry of theprotrusions 70,75, the flow of the coolant fluid 60, and the manner inwhich the protrusions 70,75 direct the coolant fluid 60 to causeimpingements of the coolant fluid 60 on the first regions 64 and thesecond regions 66 of the respective outer wall 20 and the inner wall 30for cooling the outer wall 20 will be explained in the followingparagraphs.

FIG. 2 depicts an enlarged cross-sectional view of the aforementionedexemplary section 65 comprising the portion 25 of the outer wall 20 andthe portion 35 of the inner wall 30 of the aerofoil 10.

The exemplary section 65 depicted herein is located in the upper half110 of the aerofoil 10 and is furthermore proximal to the leading edge150 of the aerofoil 10 when compared to the trailing edge 160 of theaerofoil 10. The overall direction of the flow of the coolant fluid 60in the cooling channel 40 comprised in the depicted section 65 is in thedirection from the trailing edge 160 towards the leading edge 150.

For the purpose of elucidation of the exemplary section 65, twoexemplary protrusions 80,85 on the portion 25 of the outer wall 20 andtwo exemplary protrusions 70,75 on the portion 35 of the inner wall 30of the aerofoil 10 are considered. When viewed along the overalldirection of the flow of the coolant fluid 60 in the section 65, each ofthe aforementioned protrusions 70,75,80,85 comprises the following: 1.an ascending portion 170, 2. a peak 175, and 3. a descending portion180.

When viewed along the overall direction of the flow of the coolant fluid60, the ascending portions 170 of the respective protrusions 70,75 onthe inner wall 30 extends from the surface 37 on the inner wall 30 andascends in the direction towards the outer wall 20, whereas theascending portion 170 of the protrusion 80,85 on the outer wall 20extends from the surface 27 on the outer wall 20 and ascends in thedirection towards the inner wall 30. The ascending portion 170 isadvantageously both continuous and smooth, and each of the ascendingportions 170 of each of the protrusions 70,75,80,85 end at therespective peak 175 of the respective protrusions 70,75,80,85. Thecoolant fluid 60 flowing over the ascending portion 170 of each of theprotrusions 80,85 is directed towards the ascending portion 170 of theopposing protrusion 70,75 on the opposite wall 30. Subsequently, thisresults in the impingement of the coolant fluid 60 on the opposingsecond region 64 of the opposite wall 20, thereby leading to an enhancedtransfer of heat between the coolant fluid 60 and the opposite wall 20.

Additionally the flow of the coolant fluid 60 over the ascending portion170 of the protrusion 70,75 results in accelerating the coolant fluid60. Therewith the velocity of the coolant fluid 60 is increased. Ahigher impact upon the impingement of the coolant fluid 60 on theascending portion 170 of the protrusion 80,85 on the opposing wall 20 isachieved, which enhances the transfer of heat from the wall 20 to thecoolant fluid 60.

When viewed along the overall direction of the flow of the coolant fluid60, the descending portion 180 of the protrusion 70,75 on the inner wall30 descends from the respective peak 175 and in the direction towardsthe inner wall 30 itself, whereas the descending portion 180 of theprotrusion 80,85 on the outer wall 20 descends from the respective peak175 and in the direction towards the outer wall 20 itself. Herein, theabsolute values of the respective gradients of the descending portions180 of each of the respective protrusions 70,75,80,85 are advantageouslygreater than the absolute values of the gradients of the ascendingportions 170 of each of the respective protrusions 70,75,80,85, i.e. theascending portion 170 ascends gradually and the descending portion 180descends abruptly.

The profile of the ascending portion 170 may be linear, logarithmic,exponential, quadratic, and the like. Similarly, the profile of thedescending portion 180 may be linear, logarithmic, exponential,quadratic, and the like. However, the profiles of all the protrusions70,75,80,85 are essentially the same.

The peak 175 of each of the protrusions 70,75,80,85 lies between therespective ascending portion 170 and the respective descending portion180 of the protrusion 70,75,80,85. The gradient of the protrusion70,75,80,85 is zero at its peak 175. The local flow direction of thecoolant fluid 60 constantly changes as the coolant fluid flows along theascending portions 170 of the respective protrusions 70,75,80,85. Thelocal flow at the peak 175 of the respective protrusions 70,75,80,85 isin the direction towards the respective opposing region 64,66 of theopposing wall 20,30, whereon the coolant fluid 60 impinges.

The flow of the coolant fluid 60 over the protrusions 70,75,80,85 mayalso create vortices of the coolant fluid 60 flow depending on theprofiles of the respective protrusions 70,75,80,85. Herein the usuallylaminar flow of the coolant fluid 60 is converted into a turbulent flow,akin to a turbolator effect, thereby resulting in better transfer ofheat between the coolant fluid 60 and the inner wall 30 and outer wall20 of the aerofoil 10.

The overall direction of the flow of the coolant fluid 60 is representedherein by a tangent ‘X’ 190, which is tangential to the portion 25 ofthe outer wall 20 that is comprised in the section 65. The peaks 175 ofthe protrusions 70,75,80,85 depicted in the section 65 are projected onto the tangent ‘X’ 190 by dropping perpendiculars from the peaks 175 onto the tangent ‘X’ 190, thereby resulting in the positions X₁, X₂, X₃and X₄ of the peaks 175 on the tangent ‘X’. Therein X₁ and X₃ are thepositions of the peaks 175 of the respective exemplary protrusions 80,85on the outer wall 20, and wherein X₂ and X₄ are the positions of thepeaks 175 of the respective exemplary protrusions 70,75 on the innerwall 30.

The respective protrusions 70,75,80,85 on any of the walls 20,30 areadvantageously and substantially equidistant from one another, i.e. thedistance between the neighbouring peaks 175 of the respectiveprotrusions 70,75,80,85 are substantially equal when viewed along theoverall direction of flow of the coolant fluid 60. For example, thedistance between the peaks X₁ and X₃ 175 of the protrusions 80,85 willbe identical to the distance between any two neighbouring peaks 175 ofthe respective protrusions 80,85 on the outer wall 20 of the aerofoil10. Herein, it may be noted that the distance between the protrusions70,75 on the inner wall 30 may differ slightly when compared to thedistance between the protrusions 80,85 on the outer wall 20. This can beattributed to the slightly different curvatures and radii of the innerwall 30 and the outer wall 20. Also, the distances between theprotrusions 70,75 on the inner wall 30 may vary slightly due to thevariation in curvature of the inner wall 30, and the same reason is alsovalid for the outer wall 20. However, the distances between therespective protrusions 70,75,80,85 of the respective walls 20,30 aresubstantially equal when considered section wise.

Furthermore, the protrusions 70,75 on one wall 30 and the protrusions80,85 on the opposing wall 20 are offset, i.e. they are not directlyopposite from one another, when viewed along the overall direction offlow of the coolant fluid 60. I.e. a peak 175 of a protrusion 80,85 onthe outer wall 20 and a peak 175 of a protrusion 70,75 on the inner wall30 are advantageously not directly opposite to one another. For example,X₁ and X₂ are not directly opposite to one another and the same appliesto X₃ and X₄. Additionally, the peak X₂ is located in between peaks X₁and X₃ when viewed along the tangent ‘X’ 190, advantageously midway ofpeaks X₁ and X₃. Similarly, the peak X₃ is located in between peaks X₂and X₄ when viewed along the tangent ‘X’ 190, advantageously midway ofpeaks X₂ and X₄.

The locations of the protrusions 80,85 on the outer wall 20 relative tothe locations of the protrusions 70,75 on the inner wall 30 are suchthat the first and second regions 64,66 onto which the coolant fluid 60impinges are each located between the peaks 175 of the respectiveprotrusions 70,75,80,85 of the respective outer and inner walls 30, 20.I.e. the first regions 64 on the outer wall 20 are located between thepeaks X₁ and X₃ 170 of the protrusions 80,85 of the outer wall 20,whereas the second regions 66 on the inner wall 30 are located betweenthe peaks X₂ and X₄ 170 of the protrusions 70,75 of the inner wall 30.

Herein, the individual locations of the protrusions 70,75,80,85 aremeant to be the individual positions of the protrusions 70,75,80,85 inthe overall direction of the flow of the coolant fluid 60.

Advantageously, the first and second regions 64,66 onto which thecoolant fluid 60 impinges are the respective protrusions 70,75,80,85 ofthe opposing walls 20,30. Especially, the first region 64 and the secondregion 66 are the ascending portions 170 of the respective protrusions70,75,80,85. The coolant fluid 60 ascends along the ascending portion170 of a protrusion 70 and the direction of the coolant fluid flowchanges at the peak 175 of the protrusion 70,75,80,85. Thereafter thecoolant fluid 60 is directed towards the ascending portion 170 of theopposing protrusion 80 on the opposite wall 30, whereon it impingesthereby leading to a transfer of heat from the opposite wall 20 to thecoolant fluid 60. Therewith, the aforementioned first regions 64 and thesecond regions 66 can be the respective ascending portions of therespective protrusions 70,75,80,85. Herein, the impingement of thecoolant fluid 60 on the outer wall 30 leads to the transfer of heat fromthe outer wall 20 to the coolant fluid 60, whereas the impingement ofthe coolant fluid 60 and the inner wall 30 leads to the transfer of heatfrom the coolant fluid 60 to the inner wall 30. The bulk of transfer ofheat always occurs at the ascending portion 170 of the protrusion70,75,80,85 upon the impingement of the coolant fluid 60 on theprotrusion 70,75,80,85.

Herein the protrusions 70,75,80,85 may be provided on the outer wall 20and the inner wall 30 by means of precision casting, laser sintering,electrical discharge machining, et cetera.

FIG. 3 depicts a flowchart of a method for construction of the aerofoil10.

In a step 200, the inner wall 30 and the outer wall 20 of the aerofoil10 are arranged opposing one another. The arrangement of the walls 20,30is such that the aforementioned cooling channel 40 is formed between theinner wall 30 and the outer wall 20, wherein the cooling channel 40separates the inner wall 30 and the outer wall 20.

In a step 210, the inner wall 30 is provided with protrusions 70,75. Theprotrusions 70,75 on the inner wall 30 extend from the surface 37 andalso into the cooling channel 40 and in the direction towards the outerwall 20. Additionally, the outer wall 20 is also provided with theprotrusions 80,85. The protrusions 80,85 on the outer wall 20 alsoextend both from the surface 27 and also into the cooling channel 40 andin the direction towards the inner wall 30. The arrangement of the innerwall 30 and the outer wall 20 is such that the peaks 175 of theprotrusions 70,75 of the inner wall 30 and the peaks 175 of theprotrusions 80,85 of the outer wall 20 are offset with respect to eachother in the direction of flow of the coolant fluid 60.

Herein the protrusions 70,75 on a certain wall 30 may be provided atcertain predefined locations depending on the regions 64 on the opposingwall 20 whereon the coolant fluid 60 is to be precisely impinged, inorder to cool the regions 64 on the opposing wall. These regions 64 maybe hotspots on the outer wall 20, which undergo intense heating upon theexposure of the aerofoil 10 to the hot gases 50. These hotspotsprimarily occur at the leading edge 150 of the aerofoil 10. Herewith theflow of the coolant fluid 60 over the protrusions 70,75,80,85 on theinner wall 30 is precisely directed to cause impingements of the coolantfluid on the hotspots.

Thereafter the coolant fluid 60 may be dispensed in the cooling channel40. The course of the coolant fluid 60 in the cooling channel 40 isherein influenced by the profiles of the protrusions 70,75 on the innerwall 30 and the protrusions 80,85 on the outer wall 20.

The coolant fluid 60 that flows over any of the protrusions 70,75 on theinner wall 30 is directed towards the outer wall 20, thereby leading toimpingement of the coolant fluid 60 on the region 64 of the outer wall20. The impingement of the coolant fluid 60 on the outer wall 20 leadsto a transfer of heat from the outer wall 20 to the coolant fluid 60.Therewith, cooling of the outer wall 20 is achieved. Similarly, thecoolant fluid 60 that flows over any of the protrusions 80,85 on theouter wall 20 is directed towards the inner wall 30, thereby leading toimpingement of the coolant fluid 60 on the region 66 of the inner wall30. The impingement of the coolant fluid 60 on the inner wall 30 leadsto a transfer of heat from the coolant fluid 60 to the inner wall 30.Therewith, the coolant fluid 60 is cooled in order to be redirectedagain on to the outer wall 20 for further cooling of the outer wall 20.

Though the invention has been described herein with reference tospecific embodiments, this description is not meant to be construed in alimiting sense. Various examples of the disclosed embodiments, as wellas alternate embodiments of the invention, will become apparent topersons skilled in the art upon reference to the description of theinvention. It is therefore contemplated that such modifications can bemade without departing from the embodiments of the present invention asdefined.

1-11. (canceled)
 12. An aerofoil comprising: an outer wall and an innerwall, and a cooling channel located between the outer wall and the innerwall for guiding a coolant fluid during operation of the aerofoil,wherein the inner wall comprises a protrusion on the inner wallextending from a surface of the inner wall into the cooling channel,wherein the protrusion on the inner wall is arranged and profiled suchthat the protrusion on the inner wall directs at least a part of thecoolant fluid, when the coolant fluid is flowing through the coolingchannel and over the protrusion on the inner wall, for impinging thecoolant fluid on to a first region of the outer wall, wherein the outerwall further comprises a protrusion on the outer wall, wherein theprotrusion on the outer wall extends from a surface of the outer wallinto the cooling channel, and wherein the protrusion on the outer wallis arranged and profiled such that the protrusion on the outer walldirects at least a part of the coolant fluid, when the coolant fluid isflowing through the cooling channel and over the protrusion on the outerwall, for impinging on to a second region of the inner wall.
 13. Theaerofoil according to claim 12, wherein the protrusion on the inner wallextends both in a direction of flow of the coolant fluid and in adirection towards the outer wall.
 14. The aerofoil according to claim12, wherein in an overall direction of flow of the coolant fluid, theprotrusion on the inner wall comprises: an ascending portion ascendingin a direction towards the outer wall, a descending portion descendingin a direction towards the inner wall, and a peak located between theascending portion and the descending portion, wherein an absolute valueof a gradient of the descending portion is greater than an absolutevalue of a gradient of the ascending portion.
 15. The aerofoil accordingto claim 12, wherein the protrusion on the inner wall is locatedproximal to a leading edge of the aerofoil compared to a trailing edgeof the aerofoil.
 16. The aerofoil according to claim 15, wherein theprotrusion on the outer wall extends both in the direction of flow ofthe coolant fluid and in a direction towards the inner wall.
 17. Theaerofoil according to claim 12, wherein in the overall direction of flowof the coolant fluid, the protrusion on the outer wall comprises: anascending portion ascending in a direction towards the inner wall, adescending portion descending in a direction towards the outer wall, anda peak located between the ascending portion and the descending portion,wherein for the protrusion on the outer wall, an absolute value of agradient of the descending portion is greater than an absolute value ofa gradient of the ascending portion.
 18. The aerofoil according to claim17, wherein the protrusion on the outer wall and the protrusion on theinner wall are located in the overall direction of flow of the coolantfluid such that the part of coolant fluid that is directed towards thefirst region of the outer wall by the protrusion on the inner wallimpinges on the ascending portion of the protrusion on the outer wall.19. The aerofoil according to claim 16, wherein in the overall directionof flow of the coolant fluid, the peak of the protrusion on the innerwall and the peak of the protrusion on the outer wall are offset to oneanother.
 20. The aerofoil according to claim 19, wherein the protrusionon the outer wall is located proximal to the leading edge of theaerofoil.
 21. A method for construction of an aerofoil, wherein theaerofoil comprises: an outer wall and an inner wall, and a coolingchannel located between the outer wall and the inner wall such that thecooling channel separates the outer wall and the inner wall for guidinga coolant fluid during operation of the aerofoil, wherein the inner wallcomprises a protrusion for directing at least a part of the coolantfluid, when the coolant fluid is flowing through the cooling channel,for impinging the coolant fluid on a first region of the outer wall,wherein the protrusion on the inner wall extends from a surface of theinner wall into the cooling channel, wherein the outer wall furthercomprises a protrusion, and wherein the protrusion on the outer wallextends from a surface of the outer wall into the cooling channel, themethod comprising: arranging the outer wall and the inner wall such thatthe cooling channel separates the outer wall and the inner wall,providing the protrusion on the inner wall such that the protrusion onthe inner wall extends from the surface of the inner wall into thecooling channel, and providing the protrusion on the outer wall suchthat the protrusion on the outer wall extends from the surface of theouter wall into the cooling channel for directing at least a part of thecoolant fluid, when the coolant fluid is flowing through the coolingchannel and over the protrusion on the outer wall, for impinging on to asecond region of the inner wall.